Electronic device

ABSTRACT

The electronic device ( 10 ) of the invention has a first inductor ( 12 ) and a first capacitor ( 11 ). The capacitor ( 11 ) comprises a first capacitor electrode ( 21 ) in a first electrically conducting layer ( 3 ), a dielectric ( 26 ), and a second capacitor electrode ( 25 ) in a second electrically conducting layer ( 7 ). The second conductive layer ( 7 ) also comprises the first inductor ( 12 ) and a via ( 13 ). In order to get a resonance frequency with a low tolerance, which can be used at high frequencies in RF equipment, the second capacitor electrode ( 25 ) has a contour whose projection onto the first conductive layer ( 3 ) lies within the first capacitor electrode ( 21 ). In this way the decrease in capacitance of the first capacitor ( 11 ) due to etching can be leveled out against the increase in inductance of the first inductor ( 12 ) due to the same etching. Preferably, the dielectric ( 26 ) has a middle zone ( 24 ) and edge zones ( 22, 23 ). The dielectric consists of a layer of dielectric material ( 5 ) in the middle zone ( 24 ). In the edge zones ( 22, 23 ), the dielectric consists of the layer of dielectric material ( 5 ) and a layer of electrically insulating material ( 4 ).

[0001] The invention relates to an electronic device provided with afirst coil and a first capacitor which has a first and a secondcapacitor electrode and a dielectric, which device comprises a substratewith a first and a second side, at which second side the following arepresent:

[0002] a first electrically conducting patterned layer in which thefirst capacitor electrode is defined,

[0003] a layer of dielectric material which constitutes at least in partthe dielectric, and

[0004] a second electrically conducting patterned layer comprising afirst pattern which is substantially the first coil and a second patternwhich is at least a portion of the second capacitor electrode.

[0005] Such a device is known from M. de Samber & L. Tegelaers, PhilipsJournal of Research, 51 (1998), 389-410. The known device is an LCfilter. The substrate comprises silicon with an electrically insulatingsurface of SiO₂ at the second side. The first electrically conductinglayer comprises aluminum. The second electrically conducting layer maycomprise aluminum and gold. If this layer comprises aluminum, the layerwas provided by means of sputtering and subsequent etching. A secondelectrically conducting patterned layer of gold is manufactured in thata resist layer is provided on a thin gold layer, the resist layer isstructured by means of photolithography, and the gold iselectrochemically grown.

[0006] A disadvantage of the known device is that the LC filter has aresonance frequency having a margin of error owing to uncontrollablesteps in the manufacture of the device. This margin of error is toogreat for high-frequency applications of the device.

[0007] It is a first object of the invention to provide an electronicdevice of the kind mentioned in the opening paragraph which has aresonance frequency with a margin of error which is sufficiently smallfor applications of the device at high frequencies.

[0008] This object is achieved in that:

[0009] the dielectric has a middle zone and edge zones parallel to thesecond side of the substrate,

[0010] the dielectric has a greater dielectric thickness in the edgezones than in the middle zone, and

[0011] a perpendicular projection of the second capacitor electrode ontothe first electrically conducting layer lies at least partly within thefirst capacitor electrode.

[0012] The resonance frequency of the first order is equally stronglydependent on the inductance of a coil present and on the capacitance ofa capacitor present. Owing to the greater dielectric thickness—definedas the ratio of the thickness of the layer to the dielectric constant—anincrease in the inductance owing to a badly controllable step in themanufacture of the device is compensated by a decrease in thecapacitance in that same step in the manufacture. The badly controllablestep usually is the patterning of the second electrically conductinglayer, because this layer preferably has a comparatively greatthickness. This patterning may take place, for example, through wet ordry etching or in a process in which a pattern is electrochemicallyenhanced. A similar compensation may occur if the inductance decreases:the capacitance then increases.

[0013] It is necessary in the case of a varying capacitance that aperpendicular projection of the second capacitor electrode onto thefirst electrically conducting layer lies at least partly within thefirst capacitor electrode. The perpendicular projection need not lieentirely within the first capacitor electrode; an electricallyconducting connection from the second electrode to other parts of thedevice, such as the first coil, may be present in the secondelectrically conducting layer. The compensation may also require thatthe perpendicular projection lies only partly within the first capacitorelectrode. Preferably, the ratio of the dielectric thickness in the edgezones to that in the middle zone lies between 3 and 20.

[0014] The result is that the resonance frequency of the device is notinfluenced by the error tolerances in the manufacture of the device. Thedevice, which may be not just an LC filter, but also, for example, anintegrated circuit provided with a coil and a capacitor, is suitable forapplication in RF cordless communication products such as mobiletelephones which operate at frequencies above 100 MHz. The use of theelectronic device according to the invention in a high-frequencyapplication renders it possible to adjust the frequency with a moreaccurate bandwidth. The high-frequency application thus has a betterperformance. It is also possible to use very high frequencies, such asfrequencies of more than 2000 MHz.

[0015] In a favorable embodiment

[0016] the dielectric in the middle zone is built up from the layer ofdielectric material, and

[0017] the dielectric in the edge zones is built up from the layer ofdielectric material and a layer of electrically insulating material.

[0018] The difference in dielectric thickness between the edge zones andthe middle zone can be greater owing to the combination of the layer ofdielectric material and the layer of electrically insulating material inthe edge zones than if only the layer of dielectric material werepresent.

[0019] In another embodiment of the device according to the invention

[0020] an electrically conducting patterned intermediate layer ispresent between the layer of dielectric material and the layer ofelectrically insulating material, in which intermediate layer a planarconductor track is defined which is in electrical contact with thesecond pattern of the second electrically conducting layer and forms thesecond capacitor electrode in conjunction with this pattern, and

[0021] a perpendicular projection of said second pattern onto theintermediate layer lies at least partly outside the conductor track.

[0022] In this embodiment, the layer of dielectric material is presentbetween the layer of electrically insulating material and the firstelectrically conducting layer. This has the advantage that the layer ofdielectric material and the intermediate layer were depositedconsecutively and that the boundary surface between these layers is notinfluenced by etching means. The intermediate layer serves as an etchstop layer during etching of the layer of electrically insulatingmaterial, the latter lying partly on the intermediate layer and partlyon the layer of dielectric material.

[0023] In a specific modification of the above embodiment, the layers ofdielectric material and electrically insulating material are locallyabsent outside the first capacitor, and an electrically conductiveconnection is present between the first and the second electricallyconducting layer. Such a connection is known as a via. The modifiedembodiment has the advantage that it can be manufactured withoutadditional steps in the manufacturing method. Etching of the layer ofelectrically insulating material outside the first capacitor, where nointermediate layer is present, at the same time removes the layer ofdielectric material. The subsequent deposition of the secondelectrically conducting layer then completes the via.

[0024] It is favorable, furthermore, when the second electricallyconducting layer has a thickness greater than 5 μm. The losses of thefirst coil are small in the case of such a thickness.

[0025] Preferably, the second electrically conducting layer comprisesaluminum. This material is easy to provide by sputtering and can bepatterned through wet etching. Underetching takes place in this case,which causes the capacitance of the first capacitor to decrease, whilethe inductance of the first coil increases. Furthermore, aluminum has agood conductivity. This is important not only for the coil but also forthe conductor tracks or interconnects, which are preferably defined inthe second electrically conducting layer.

[0026] The first electrically conducting layer comprises, for example,aluminum, doped poly(3,4-ethylenedioxy)thiophene, polyaniline, nickel,copper, gold, platinum, or doped silicon.

[0027] The material of the substrate may be chosen from a large numberof materials. Examples are glass, alumina, polyimide, and silicon.Preferably, high-ohmic silicon, which is oxidized to silicon oxide atthe second side, is chosen on account of the high-frequency application.

[0028] Preferably, the dielectric material is a material having a highdielectric constant. Examples are silicon nitride, substituted bariumtitanate and barium niobate, tantalum oxide, and polyvinylphenol.Preferably, the electrically insulating material is a material having alow dielectric constant such as silicon oxide, polyimide,benzocyclobutene. The electrically insulating material may possibly bepatterned by means of photolithography.

[0029] These and other aspects of the invention will be explained inmore detail with reference to drawings, in which:

[0030]FIG. 1 is a diagrammatic side elevation of a first embodiment ofthe device according to the invention; and

[0031]FIG. 2 is a diagrammatic side elevation of a second embodiment ofthe device according to the invention.

[0032] Embodiment 1

[0033] The LC filter 10 in FIG. 1 has a substrate 1 of Al₂O₃ with a fistside 41 and a second side 42, of the substrate 1, there is a firstelectrically conducting layer 3 of Ni in which a first capacitorelectrode 21 is defined. Also present in the first electricallyconducting layer 3 is a conductor track 27 which connects a via 13—andthereby inter alia a first coil 12—to a U-shaped electrical contact 14.A dielectric 26 lies on the first capacitor electrode of the firstcapacitor 11. In the edge zones 22 and 23 of the capacitor 11, thedielectric 26 comprises a layer of dielectric material 5 of 0.01 to 0.2μm thickness and a layer of electrically insulating material 4 of 0.1 to0.8 μm thickness. The dielectric 26 comprises the layer of dielectricmaterial 5 in the middle zone 24 of the capacitor 11. The dielectricmaterial is BaNdTiO₃. The electrically insulating material is SiO_(x),1≦×≦2. A second electrically conducting layer 7 of Al is present on thelayer of dielectric material 5. The second capacitor electrode 25 of thefirst capacitor 11, the first coil 12, and a vertical interconnect area(via) 13 are defined in this second electrically conducting layer 7,which has a thickness of 4 to 7 μm. The first coil 12 is the firstpattern, the second capacitor electrode is the second pattern. Aperpendicular projection of the second capacitor electrode 25 onto thefirst conducting layer 3 lies within the first electrode 21. The factthat underetching occurs during etching of holes 31, 32, and 33 in thesecond conducting layer 7 causes the surface area of the secondcapacitor electrode 25 to decrease, and thus also the capacitance valueof the first capacitor 11. At the same time, the inductance value of thefirst coil 12 increases. The second conducting layer 7 is covered with aprotective layer 8.

[0034] Embodiment 2

[0035] The electronic device 110 in FIG. 2 comprises a substrate 1 ofsilicon with a first side 41 and a second side 42. At the second side42, the substrate 1 is covered with an electrically insulating layer 2of silicon oxide. A first electrically conducting layer 3 of Al, inwhich a first capacitor electrode 21 of the first capacitor 11 isdefined, is present on the layer 2. A layer of dielectric material 5,which is removed at the area of the via 13, lies on the firstelectrically conducting layer 3. The layer of dielectric material 5comprises SiN_(x), 0.5≦×≦2, and constitutes the dielectric 26 in amiddle zone 24 of the capacitor 11. In the edge zones 22 and 23, thedielectric 26 comprises not only the layer of dielectric material 5 butalso a layer of electrically insulating material 4, in this exampleSiO_(x), 1≦×≦2. An intermediate layer 6 comprising Al lies on the layerof dielectric material 5 and is partly covered by the layer ofelectrically insulating material 4. A conductor track 28 is defined inthe intermediate layer 6. A second pattern 29 of a second electricallyconducting layer 7, also comprising Al, is in electrical contact withthis conductor track 28. The conductor track 28 and the second pattern29 together form the second capacitor electrode 25 of the firstcapacitor 11. The second conducting layer 7 in addition comprises afirst coil 12 as a first pattern, a via 13, and an interconnect 14, andis covered with a protective layer 8. A perpendicular projection of thesecond pattern 29 onto the intermediate layer 6 lies partly outside theconductor track 28. A perpendicular projection of the second pattern 29onto the first conducting layer 3 lies partly outside the firstcapacitor electrode 21, i.e. at the area of the interconnect 14. Thisinterconnect 14 is necessary for connecting the second capacitorelectrode 25 to other parts of the device 110. Hence, a perpendicularprojection of the second capacitor electrode 25 onto the firstconducting layer 3 lies at least partly inside the first capacitorelectrode 21.

1. An electronic device (10, 110) provided with a first coil (12) and afirst capacitor (11) which has a first (21) and a second capacitorelectrode (25) and a dielectric (26), which device (10) comprises asubstrate (1) with a first (41) and a second side (42), at which secondside (42) of the substrate (1) the following layers are present: a firstelectrically conducting patterned layer (3) in which the first capacitorelectrode (21) is defined, a layer of dielectric material (5) whichconstitutes at least in part the dielectric (26), and a secondelectrically conducting patterned layer (7) comprising a first patternwhich is substantially the first coil (12) and a second pattern which isat least a portion of the second capacitor electrode (25), characterizedin that: the dielectric (26) has a middle zone (24) and edge zones (22,23) parallel to the second side of the substrate (1), the dielectric(26) has a greater dielectric thickness in the edge zones (22, 23) thanin the middle zone (24), and a perpendicular projection of the secondcapacitor electrode (25) onto the first electrically conducting layer(3) lies at least partly within the first capacitor electrode (21). 2.An electronic device (10, 110) as claimed in claim 1, characterized inthat the dielectric (26) in the middle zone (24) is built up from thelayer of dielectric material (5), and the dielectric (26) in the edgezones (22, 23) is built up from the layer of dielectric material (5) anda layer of electrically insulating material (4).
 3. An electronic device(110) as claimed in claim 1, characterized in that an electricallyconducting patterned intermediate layer (6) is present between the layerof dielectric material (5) and the layer of electrically insulatingmaterial (4), in which intermediate layer (6) a planar conductor track(28) is defined which is in electrical contact with the second pattern(29) of the second electrically conducting layer (7) and forms thesecond capacitor electrode (25) in conjunction with this pattern (29),and a perpendicular projection of said second pattern (29) onto theintermediate layer (6) lies at least partly outside the conductor track(28).
 4. An electronic device (10, 110) as claimed in claim 3,characterized in that the layers of dielectric material (5) andelectrically insulating material (4) are locally absent outside thefirst capacitor (11), and an electrically conductive connection (13) ispresent between the first (3) and the second electrically conductinglayer (7).
 5. An electronic device (10, 110) as claimed in claim 1,characterized in that the second electrically conducting layer (7) has athickness greater than 5 μm.
 6. An electronic device (10, 110) asclaimed in claim 1, characterized in that the second electricallyconducting layer (7) comprises aluminum.
 7. The use of the electronicdevice as claimed in claim 1 (10, 110) for a high-frequency application.